As a communication system (in-vehicle network) that is attached to a vehicle and performs a differential communication, CAN (Controller Area Network, a registered trademark) whose maximum communication speed is approximately 1 Mbps is known.
CAN-FD (CAN with Flexible Data-Rate, a registered trademark), which is capable of performing higher speed communication than CAN, is also known. Maximum communication speed of CAN-FD is approximately 8 Mbps.
In a frame configuration of CAN-FD, areas of data and CRC (Cyclic Redundancy Check) are accelerated and the remaining areas are the same as CAN. With this configuration, CAN-FD is capable of performing the differential communication at higher speed than CAN with a common transmission path used.
Related to the vehicle, further acceleration of the in-vehicle network is required due to an increase of attached electronic control apparatuses (ECU: Electronic Control Unit).
As an example of communication system that is capable of performing high speed communication, Ethernet (Ethernet: a registered trademark) is widely known. To meet the above-described requirement, Ethernet that has communication speed of approximately 100 Mbps may be employed in the in-vehicle network.
Ethernet is different in a characteristic of physical layer and protocol from CAN or CAN-FD. In a vehicle that has constructed network under CAN or CAN-FD, in order to construct Ethernet for high speed communication in addition, an exclusive communication line needs to be wired.
Alternatively, a communication technique transmitting a first signal (voice data) as an in-phase signal, and a clock signal synchronized with the first signal as a differential signal, is proposed. In this configuration, the communication is made on the transmission path configured by a pair of the communication lines (for example, see Patent Literature 1).